<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>

    <script type="text/javascript">
        var i;
        //alert(i);//undefined
        i = 12;
        //typeof()是JavaScript语言提供的一个函数
        alert(typeof(i));

        i = "abc";
        alert(typeof i);//String

        var a = 12;
        var b = "abc";
        alert(a *b);
        

    </script>


</head>
<body>

</body>
</html>